1. Field of the Invention
The present invention relates to golf balls, and more particularly, to solid golf balls including a core comprising a crosslinked rubber, and a cover comprising a resin composition.
2. Description of the Related Art
Golf balls used for playing golf at a golf course are generally classified as: wound golf balls having a core comprising wound rubber threads; and solid golf balls (two-piece golf balls, three-piece golf balls, and the like) having a core comprising a solid rubber. Wound golf balls have been conventionally used, with a period through which wound golf balls account for almost all of the first-class golf balls. However, solid golf balls that have been developed afterwards can be readily manufactured at a lower cost, therefore, larger number of solid golf balls have been recently supplied to the market than the wound golf balls. In general, feel at impact of the wound golf ball is soft, and thus, among the professional golfers as well as the senior-class amateur golfers, there still exist strong needs for the wound golf balls that are excellent in feel at impact in spite of the current status where solid golf balls prevail at the market.
Meanwhile, various attempts have been made to improve feel at impact and a travel distance of solid golf balls (for example, see Japanese Patent Publication References H6-319831/1994, H10-248958/1998, H11-128403/1999, 2000-512881, and the like). In recent years, solid golf balls have been developed, which exhibit feel at impact nearly as soft as that of wound golf balls.
In the meantime, USGA (United States Golf Association) has defined a rule for an initial velocity of a golf ball. In accordance with this rule, the initial velocity of a golf ball as measured with a flywheel initial velocity measuring machine under a predetermined condition should not be higher than 255 ft/s. The golf balls out of this order cannot be officially approved by USGA, which are not accepted for use in official games all over the world.
USGA also defines a rule of ODS. In accordance with this rule, a travel distance of a golf ball should be equal to or less than 280 yards when hit with a predetermined condition. The golf balls out of this order cannot be officially approved by USGA, which are not accepted for use in official games all over the world.
A golf ball is hit by an impact with a golf club. The initial velocity upon the hit does not necessarily correlate to the initial velocity according to a flywheel method. In particular, solid golf balls, of which feel at impact being nearly as soft as wound golf balls, tend to represent high initial velocity according to a flywheel method despite the fact that the actual velocity is not that high upon the hit by a golf club. In view of the observance of USGA rules, golf ball manufacturers may intentionally use materials that provide inferior resilience performance with the solid golf ball having soft feel. When such a golf ball is hit by a golf club, tendencies to result in lower initial velocity, lower launch angle, larger backspin speed, and the like are exhibitted. Consequently, sufficient travel distance may not be achieved. Especially, insufficient travel distance is apt to be achieved when golfers who are playing with a lower clubhead speed (e.g., woman golfers and average golfers) hit the ball.
Apart from the golfers who play in official games, many ordinary golfers play golf for their pleasure. These ordinary golfers desire golf balls having excellent flight performance, which allow pleasant game playing accordingly. For such ordinary golfers, it is not that important concern whether the golf balls conform to USGA rules or not.
The present invention was accomplished in light of such circumstances, and the object of the present invention is directed to provide solid golf balls having soft feel at impact, and an excellent resilience performance and an excellent flight performance.